Lung cancer is the leading cause of death due to cancer in the United States, killing approximately 156,000 men and women each year. There are four major bronchogenic carcinoma cell types that account for over 95% of primary lung cancers: adenocarcinoma; squamous cell carcinoma; large cell carcinoma; and small cell carcinoma. These cell types occur singly or in combination. The remaining 5% of tumors are composed of several unusual tumor types.
When lung cancer develops, it tends to spread from the original cancer site to the lymph nodes, and then, either at the same time or sequentially, to other areas of the body. The most common sites for lung cancer to spread (metastasis) are the brain, bones, liver, adrenal glands, and any other organ with a high rate of blood flow. It is this process of metastasis that leads to fatality in most patients.
When a cancer is first discovered by physical examination or by diagnostic tests (e.g., X-ray or high resolution imaging such as spiral CT), it is usually at least 1 cm in size. A cancer that is 1 cm in size contains at least about 1 billion cells.
Changes in chromosomal DNA have been shown to accompany the conversion of normal cells to malignant cells. Because of this, detection of specific chromosomal alterations provides a route to detecting and diagnosing lung cancer.